Forms of soluble aluminium in acidic topsoils estimated by ion chromatography and 8-hydroxyquinoline and their correlation with growth of subterranean clover

SUMMARY Labile Al in the soil solution measured by 8-hydroxyquinoline (AlHQ) was a better predictor of plant growth than trivalent Al (AlIC3+) measured by ion chromatography (IC). HQ reacted with some organic Al complexes which did not separate during chromatography. In the presence of oxalic acid, AlHQ was greater than AlIC3+, which was the same as the greater than Al3+ (Al3+Calc), whereas in the presence of citric acid, AlHQ was greater than AlIC3+, and both were greater than Al+3Calc, In extracts of soils that had been acidified, Al3+IC was less than AlHQ, which was similar to Al3+Calc, when it was assumed that the only complexing ligands were OH− and F−. The proportion of Al3+IC in the soil solutions decreased more than AlHQ as the pH increased. Organic ligands appeared to form complexes with Al at the expense of AIF complexes. Forms of Al detected by IC differed in CaCl2 extracts and soil solutions. AlHQ in the CaCl2 extracts and soil solution were closely correlated, although the proportion of AlHQ was higher in the CaCl2 extracts. And soil solutions. AlHQ in the CaCl2 extracts and soil solution were closely correlated, although the proportion of AlHQ was higher in the CaCl2 extracts.